The preparation of di(aminoaryl) methanes and mixtures of methylene-bridged polyaryl polyamines containing the di(aminoaryl) methanes, by the acid condensation of aromatic amines and formaldehyde is well-known in the art (see e.g., U.S. Pat. No. 2,683,730). The di(aminoaryl) methanes and the polyamine mixtures are useful as intermediates in the preparation of the corresponding di- and polyisocyanates.
The di(aminoaryl) methanes prepared by procedures commonly used in the art generally consist mainly (i.e., 90 percent by weight or more) of the 4,4'-isomer with relatively minor amounts (i.e., less than 10 percent by weight) of the corresponding 2,4'-isomer. Recently, interest has been shown in di(aminoaryl) methanes containing higher amounts of the 2,4'-isomer. Various procedures have been suggested for the production of such high 2,4'-isomer content materials. Illustrative are the techniques described in U.S. Pat. No. 3,362,979 (process using acidic siliceous catalyst); 3,277,173 (process conducted in the presence of controlled amounts of water); 3,857,890 (removal of acid after aminobenzylamine formation); and 4,071,558 (process using specified catalyst); and Belgian Pat. No. 648,787 (process using controlled temperatures).
It has now been found that di(aminoaryl) methanes and methylene bridged polyaryl polyamines with substantially increased ortho-substitution can be produced using the novel procedure described herein.